Diaphragm for acoustical apparatus



Dec. 31, 1929. HECHT ET AL- 1,741,341

DIAPHRAGM FOR ACOUSTICAL APPARATUS Filed Dec. 5. 1922 W WM W Patented Dec. 31, 1929 UNITED STATES PATENT OFFICE HEINRICH HECH'I. AND WILHEL M RUDOLPH, OF KIEL, GERMANY, ASSIGNORS TO SIGNAL GESELLSGHAFT MIT BESCHRANKTER HAIETUNG, OF KIEL, GERMANY, A

FIRM

DIAPHRAGM FOB AGOUSTICAL APPARATUS Application filed December 5, 1922, Serial No. 605,031, and in Germany January 26, 1922.

This invention relates to diaphragms of acoustical apparatus, such as receivers and transmitters for sound signal apparatus, telephones, etc.

In diaphragms of such apparatus the effects of heat make themselves noticeable in two ways, as will hereinafter more fully apear. p As a rule the diaphragm itself consists of material that is difi'erent from that of the parts which support it, as for example the casing of the apparatus in which the diaphragm is mounted. When an apparatus of this kind is assembled and adjusted at a certain given temperature the stresses and curvature of the diaphragm will be changed when it is heated, because the degrees of expansion of the diaphragm and the casing will be different from each other. In practical apparatus the expansion of the diaphragm is generally greater than that of the casing so that the former, when subjected to a temperature difiering from that at which it was adjusted, will bend or be deflected. But even if the material of which thediaphragm consists and that of the casing are similar, bending or deflection of the diaphragm will occur, because the degrees of expansion will diifer on account of the different shapes of the different parts. phragm, as of a telephone receiver for instance, is very deleterious in two respects, viz it causes the gap between the diaphragm and the armature of its magnet to be changed, and besides it alters'the tuning of the diaphragm.

The object of the present invention is to obviate the above-mentioned detrimental d effects of changes of temperature. To this end a diaphragm has been provided having a central main portion and a marginal annularly corrugated spring portion, the corrugated spring portion being sufficiently flexible and so arranged as to permit it to compress and yield substantially only in the plane of the main portion to take up the radial size variations of the main portion. Since the spring portion yields substantially only in the plane of the main portion, when the mam po rtion is expanded or contracted by changes 111 peripheral corrugations This bendingof the dia- 1 temperature, the diaphragm is not deflected to one side or and its tuning is not materially altered because the variation in its effective transverse elastic force is not very great.

Another feature of the invention consists in forming the diaphragm not only with to take up expansions and contractions as aforesaid, but'also with radial grooves or ribs extending in the direction from the centre towards the periphery of. the main portion to make the latter acoustically rigid. By this means a monoresonant vibrating structure of a definite tuning is obtained.

The invention is illustrated in the drawing in which Fig. l is a plan view of one form of the improved diaphragm,

Fig. 2 is a more or less diagrammatic sectional View of the same, and

Figure 3 shows the diaphragm supported at its periphery.

' The diaphragm,as shown, is divided up into two portions, the central rigid main portion 10 and the marginal spring portion 11. The central portion 10 is made rigid, that is, acoustically rigid, by means of the radial corrugations or ribs 12 which span practicaly its entire surface. Secured to the center of the diaphragm is an armature 13 which vibrates with the diaphragm. The marginal spring portion 11 is bent to form a series of annular corrugations 14, which render this portion of the diaphragm yieldable in the plane of the main portion to take up the radial size variations of the main portion ue to temperature changes. The periphery 15 of the diaphragm is rigidly clamped by means of the clamping members 16 as shown in Fig. 3. It will be observed that the corrugations, as shown, are so formed as to extend symmetrically on both sides of the plane of the main portion, and that the outer periphery of the diaphragm or spring portion is in the plane of the mam portion. Thus, the corrugated spring portion acts more or less like a leaf spring in takin up the radial expansions and contractions o the main portion due to temperature changes.

the other of its normal position,

As stated above, the object of the invention is to keep the gap between the armature and the pole pieces of the receiver constant at various temperatures. Diaphragms of this kind have an additional advantage which is revealed in the case of instruments or apparatus in which the armature gap may be altered at will, as by shifting the magnet relatively to the diaphragm. The advantage is that by such alterations of the air gap, the diaphragms can be much more readily tuned, and that they permit of different tunings between much wider limits than ordinary flat diaphragms. The novel diaphragm is applicable to all kinds of acoustical apparatus fitted with diaphragms in which the drawbacks stated above should be prevented. This is the case wherever the diaphragm should form a well-defined acoustical, vibrating member whose behaviour, in executing vibrations, should remain constant, or in cases where it is important to maintain a constant distance between the diaphragm and a corresponding part of the apparatus in which it is fitted. Apparatus in which these requirements are important are for example microphones, relays, sound-boxes of gramophones, hooters and other sound pro ducers and receivers for all kinds of sound propagating mediums.

We claim 1. A diaphragm having an annularly corrugated marginal spring portion adapted to yield substantially only in the plane of the diaphragm to take up the radial size variations of the diaphragm due to temperature changes, and a central main portion merging directly into said marginal spring portion and stiitened over its whole surface, and peripheral clamping means, the said marginal spring portion merging directly into the portion of the diaphragm clamped between said clamping means.

2. A diaphragm having an annularly corrugated marginal spring portion adapted to yield substantially only in the plane of the diaphragm to take up the radial size variations of the diaphragm due to temperature changes, and a central main portion merging directly into said marginal spring portion and stifi'ened over substantially its whole surface by radially extending corrugations, and peripheral clamping means, the said marginal spring portion merging directly into the portion of the diaphragm clamped between said clamping means.

3. A diaphragm having a rigid main portion, and a marginal spring portion directly bounding said main portion and adapted to yield substantially only in the plane of the main portion to take up the radial size variations of the main portion due to temperature changes, the spring portion being annularly corrugated, the corrugations being arranged to extend symmetrically on both sides of the plane of the main portion, and the diaphragm being adapted to be clamped at points of said spring portion in the plane of the main portion, and clamping means, said spring portion merging directly into the portion of the diaphragm clamped between said clamping means.

4. A diaphragm having a rigid central main portion, an annularly corrugated marginal spring portion, and a peripheral plane portion directly adjacent the marginal spring portion, the corrugations of said marginal spring portion being symmetrical with the plane containing the rigid central main portion and the peripheral plane portion Whereby the radial size variations of the main portion due to temperature changes are taken up by the marginal spring portion without any substantial deflection of the diaphragm.

5. A diaphragm consisting substantially of a plane surface but for an annular spring portion near the periphery of the diaphragm, said annular spring portion being symmetrical with the plane of the diaphragm and adapted to yield to accommodate changes of size of the diaphragm due to temperature changes.

In testimony whereof we a'iiix our signatures.

HEINRICH HECHT. WILHELM RUDOLPH. 

